Premium
Arterial P O2 Values Vary Dramatically During Diving and Surface Activities in the Freshwater Turtle ( Trachemys scripta)
Author(s) -
Williams Cassondra L,
Hicks James W
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.1230.7
Subject(s) - arterial blood , oxygenation , hypoxia (environmental) , artery , turtle (robot) , respiratory system , blood flow , pulmonary artery , biology , zoology , anatomy , oxygen , chemistry , medicine , ecology , organic chemistry
Mammals and birds maintain a narrow range of arterial P O2 values to preserve near complete O 2 saturation. Since arterial blood gases in mammals and birds are tightly coupled with lung gas values, this is accomplished through changes in ventilation. In reptiles, pulmonary and system circulations are not completely separated and thus, cardiac shunts play a role in arterial blood gas values. Increases or decreases in the degree of right to left shunting (blood flow bypassing the pulmonary system) will immediately alter admixture and arterial P O2 can change rapidly despite stable ventilation. Further, anoxia‐tolerant reptiles, such as the red‐eared slider, may not need to maintain high arterial P O2 values. As a result, blood oxygen levels may vary more than in mammals and birds during diving as well as during other activities. To investigate this question, we continuously measured arterial P O2 in undisturbed, untethered red‐eared sliders ( Trachemys scripta) over a 48‐hour period. Our hypotheses were (1) during routine activities, arterial P O2 values will vary but remain at or above 40 mmHg (75% O 2 saturation) and (2) end of dive arterial P O2 values will be lower with longer submergences. Six adult red‐eared sliders (1546 ± 144g) were kept in tanks filled with 25°C water in a 25°C room. P O2 electrodes were surgically implanted in the carotid artery of anesthetized turtles. A self‐contained, waterproof data logger attached to the P O2 electrode was programmed to record P O2 at 1 Hz and epoxied to the carapace. After recovery, turtles were returned to the tank where they could freely swim and bask on a platform warmed by a heat lamp. Turtle behavior was recorded using a surveillance camera placed above the tank. Data were collected and analyzed. All procedures were approved by the University of California (IACUC #2011‐2995). Arterial P O2 during routine activities varied dramatically and individual P O2 values were often less than 40 mmHg. Mean P O2 values for each activity were: 22–42 mmHg for resting underwater; 23–55 mmHg while resting at surface; 29–49 mmHg during basking; and, 28–41 mmHg while swimming. Minimum P O2 values during surface events, basking, and swimming were often as low as minimum vales during submergences. End of submergence P O2 values varied dramatically from 2.7 to 51.7 mmHg and were significantly related to duration in only two turtles (p=0.007, 0.009). These results suggest freely diving, undisturbed T. scripta do not tightly regulate arterial O 2 levels or maintain stable high arterial P O2 values even at the surface. The drive to maintain high arterial P O2 levels may be absent in these turtles due to their high tolerance to hypoxia and minimal metabolic demands. Support or Funding Information This research was funded by NSF IOS 1121324 (to J. Hicks). C.L.W. was supported in part by a National Institute of Health grant (NIH‐NIAMS T32AR047752 to V. Caiozzo).